Phosphor screen with double layered blue phosphor and method thereof

ABSTRACT

A double layer phosphor screen comprising a panel having black matrix for a CRT and red, green and blue phosphors on the panel, wherein the phosphor is formed on which the black matrix is not formed and the blue phosphor is formed in double layers, and the CIE Y color coordinate of the blue phosphor for a first layer formed on the panel is 0.045 to 0.065, the CIE Y color coordinate of the blue phosphor for a second layer formed on the first layer is 0.075 to 0.095, improves brightness, color reproducing range and contrast.

(1) FIELD OF THE INVENTION

The present invention relates to a double layer phosphor screen and aprocess for preparing the same, particularly to a phosphor screenincluding a double layer of blue phosphor. The phosphor screen of thepresent invention shows preferable brightness, contrast and colorreproducing range.

(2) DESCRIPTION OF THE RELATED ART

In a conventional shadow-mask-type CRT (cathode ray tube), graphicimages are reproduced by red, green, and blue electron beams emittedfrom means for producing them which pass through a hole of a shadowmask, converge into a point, and collide with red, green, and bluephosphors formed on a phosphor screen of an inner surface of a panel.

The phosphor screen comprises red, green, and blue phosphors which havea pattern and black matrix which is formed on the same surface andbetween the phosphors.

Generally, a process for forming a phosphor screen takes the followingsteps.

A photoresist is coated on the inner surface of a panel, dried by heator other means, and exposed by irradiation of ultraviolet rays throughmask slots. The exposed panel is washed and developed to remove theunexposed photoresist and then dried. Black matrix materials are coatedon the panel on which the photoresist-coated portion andphotoresist-uncoated portion are regularly arranged. Then, the blackmatrix is produced by etching the panel. A phosphor screen is producedby using red, green and blue phosphors and then deposing an aluminumfilm on the panel having the black matrix.

Brightness, color reproducing range and contrast have immense effect onthe graphic image of a CRT. So continuous efforts to improve brightnessof a CRT by increasing fluorescent intensity to electron beams and toimprove contrast of a CRT by magnify reflection ratio to exterior lightshave been performed.

Meanwhile, ZnS;AgAl, ZnS;AgCl, etc. are generally used as blue phosphormaterials of the CRT. As shown in FIG. 3, the intensity of brightness isreversibly proportional to that of color coordinate (Y). Increasing thevalue of color coordinate makes the color blurred, which means that thecolor reproducing range decreased. Therefore, to improve the brightnessand the color reproducing range at the same time is always restricted.To resolve the above problems, some people make attempts to improvebrightness by adding some additives in the ZnS type blue phosphormaterial and improve contrast by attaching a filter to a panel. However,the above trials almost do not improve the performance of a CRT.Additionally, the attempt using a filter causes the process difficultand increase the production cost.

SUMMARY OF THE INVENTION

The present invention is to solve the above problems in the conventionalarts. The present invention provides a double layer phosphor screen anda process for preparing the same which shows preferable brightness,contrast and color reproducing range.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with the description, serve to explain the objects, advantages,and principles of the invention.

In the drawings:

FIG. 1 is a cross sectional view of a prior phosphor screen having red,green and blue phosphors on a black matrix-coated panel;

FIG. 2 is a cross sectional view of a phosphor screen having red, greenand blue phosphors having double layers on a black matrix-coated panelaccording to the present invention; and

FIG. 3 is a graph showing relations between brightness and colorcoordinate.

DETAILED DESCRIPTION OF THE INVENTION

To achieve the above object, the present invention provides a doublelayer phosphor screen comprising a panel having black matrix for a CRTand red, green and blue phosphors on said panel, wherein the phosphor isformed on which the black matrix is not formed and said blue phosphor isformed in double layers, and the CIE Y color coordinate of the bluephosphor for a first layer formed on the panel is 0.045 to 0.065, theCIE Y color coordinate of the blue phosphor for a second layer formed onthe first layer is 0.075 to 0.095.

The present invention also provides a process for preparing a doublelayer phosphor screen comprising the steps of forming red and greenphosphor dots on a panel having black matrix for a CRT, coating theslurry of a blue phosphor for a first layer on said panel, wherein a CIEY color coordinate of the phosphor is 0.045 to 0.065, coating the slurryof a blue phosphor for a second layer on said first layer, wherein a CIEY color coordinate of the phosphor is 0.075 to 0.095, and forming adouble layer blue phosphor dots by exposing and developing the slurry ofthe blue phosphor for said first and second layers.

It is preferable that said blue phosphor for said first layer has adiameter of 5 to 10 μm and pigments are attached to it. It is alsopreferable that said blue phosphor for said second layer has notpigments and the ratio of the thickness of said first layer to saidsecond layer is 1:2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS REPRESENTATIVEEXAMPLES

As shown in FIG. 2, red phosphor dots (R) and green phosphor dots (G)are formed on a panel (1) having black matrix dots (2) for a CRTaccording to a conventional process. After the red and green phosphorsare formed, a blue phosphor slurry (B1) which has pigments and has 0.045to 0.065 of CIE Y color coordinate is coated on the panel. Thereafter, ablue phosphor slurry (B2) which has 0.075 to 0.095 of CIE Y colorcoordinate is coated on the blue phosphor slurry (B1). Then, these twolayer of blue phosphor slurry are exposed and developed to produce ablue phosphor having a double layer. Conventional coating methods like aspin coating or a roll coating can be used in the above process. It ispreferable that the ratio of thickness of the layer (B1) to the layer(B2) is 1:2. The phosphor screen of the present invention is produced bydeposing an aluminum film on the panel on which the above red, green andblue phosphors are formed.

PREFERABLE EXAMPLES

A preferable working example and reference examples are described below.These examples are exemplary only, and the present invention is notrestricted to the scope of the example.

WORKING EXAMPLE 1

PVP-DAS, a photoresist is evenly coated with l m thickness on thesurface of a 14 inch panel for a CRT, exposed by a super high voltageHg-lamp having wavelength of 250-600 nm of ultraviolet rays for 20seconds. The exposed panel was washed with pure water, developed anddried at 25° C. for 3 minutes to produce photoresist dots. Graphitegenerally used as black matrix material was coated on the panel. Thenthe panel was exposed, developed and washed to produce black matrixdots.

Small amount of a surfactant and a dispersion agent were added to redphosphor material to produce a slurry. The slurry was coated on thepanel, dried, exposed by a super high voltage Hg-lamp and developed withwater under a low pressure to produce red phosphor dots. To producegreen phosphor dots, the above process was performed with the samemanner. After the red and green phosphor dots were formed, a bluephosphor slurry (B1) which has pigments and has 0.055 of CIE Y colorcoordinate was coated with 10 μm thickness on the panel. Thereafter, ablue phosphor slurry (B2) which has 0.093 of CIE Y color coordinate wascoated with 20 μm thickness on the blue phosphor slurry (B1). Then,these two layers of blue phosphor slurry were exposed and developed toproduce a blue phosphor having a double layer. The phosphor screen ofthe present invention was produced by deposing an aluminum film on thepanel on which the above red, green and blue phosphors were formed.

REFERENCE EXAMPLE I

As shown in FIG. 1, PVP-DAS, a photoresist is evenly coated with 1 μmthickness on the surface of a 14 inch panel (1) for a CRT, exposed by asuper high voltage Hg-lamp having wavelength of 250-600 nm ofultraviolet rays for 20 seconds. The exposed panel was washed with purewater, developed and dried at 25° C. for 3 minutes to producephotoresist dots. Graphite generally used as black matrix material wascoated on the panel. Then the panel was exposed, developed and washed toproduce black matrix dots (2).

Small amount of a surfactant and a dispersion agent were added to redphosphor material to produce a slurry. The slurry was coated on thepanel, dried, exposed by a super high voltage Hg-lamp and developed withwater under a low pressure to produce red phosphor dots (R). To producegreen phosphor dots (G), the above process was performed with the samemanner. After the red and green phosphor dots were formed, a bluephosphor slurry (B) which has 0.066 of CIE Y color coordinate was coatedwith 10 μm thickness on the panel. Thereafter, the layer of bluephosphor slurry were exposed and developed to produce a blue phosphor.The phosphor screen was produced by deposing an aluminum film on thepanel on which the above red, green and blue phosphors were formed.

REFERENCE EXAMPLE 2

PVP-DAS, a photoresist is evenly coated with 1 μm thickness on thesurface of a 14 inch panel for a CRT, exposed by a super high voltageHg-lamp having wavelength of 250-600 nm of ultraviolet rays for 20seconds. The exposed panel was washed with pure water, developed anddried at 25° C. for 3 minutes to produce photoresist dots. Graphitegenerally used as black matrix material was coated on the panel. Thenthe panel was exposed, developed and washed to produce black matrixdots.

Small amount of a surfactant and a dispersion agent were added to redphosphor material to produce a slurry. The slurry was coated on thepanel, dried, exposed by a super high voltage Hg-lamp and developed withwater under a low pressure to produce red phosphor dots. To producegreen phosphor dots, the above process was performed with the samemanner. After the red and green phosphor dots were formed, a bluephosphor slurry which has 0.093 of CIE Y color coordinate was coatedwith 10 μm thickness on the panel. Thereafter, a blue phosphor slurrywhich has pigments and has 0.055 of CIE Y color coordinate was coatedwith 20 μm thickness on the blue phosphor slurry. Then, these two layersof blue phosphor slurry were exposed and developed to produce a bluephosphor having a double layer. The phosphor screen was produced bydeposing an aluminum film on the panel on which the above red, green andblue phosphors were formed.

REFERENCE EXAMPLE 3

As shown in FIG. 1, PVP-DAS, a photoresist is evenly coated with 1 μmthickness on the surface of a 14 inch panel (1) for a CRT, exposed by asuper high voltage Hg-lamp having wavelength of 250-600 nm ofultraviolet rays for 20 seconds. The exposed panel was washed with purewater, developed and dried at 25° C. for 3 minutes to producephotoresist dots. Graphite generally used as black matrix material wascoated on the panel. Then the panel was exposed, developed and washed toproduce black matrix dots (2).

Small amount of a surfactant and a dispersion agent were added to redphosphor material to produce a slurry. The slurry was coated on thepanel, dried, exposed by a super high voltage Hg-lamp and developed withwater under a low pressure to produce red phosphor dots (R). To producegreen phosphor dots (G), the above process was performed with the samemanner. After the red and green phosphor dots were formed, a bluephosphor slurry which has 0.093 of CIE Y color coordinate and a bluephosphor slurry which has 0.055 of CIE Y color coordinate were mixed andcoated with 10 μm thickness on the panel. Thereafter, the layer of bluephosphor slurry were exposed and developed to produce a blue phosphor.The phosphor screen was produced by deposing an aluminum film on thepanel on which the above red, green and blue phosphors were formed.

Brightness and phosphor reflection ratio (contrast) of CRTs using thephosphor screens produced with the above examples were tested by aphotometer (Minolta CA-100) and the results are shown in Table 1.

                  TABLE 1    ______________________________________                         Brightness                                  Phosphor           CIE Y color coordinate                         (%)      reflection ratio    ______________________________________    Work. Exam. 1             1'st layer phosphor 0.055                             121      115             2'nd layer phosphor 0.093    Ref. Exam. 1             0.066           100      100    Ref. Exam. 2             1'st layer phosphor 0.093                             113      85             2'nd layer phosphor 0.055    Ref. Exam. 3             mixed           102      95    ______________________________________

As shown in Table 1, brightness of the double layer phosphor screen ofthe present invention increased about 20% compared with that ofReference Example 1 and the phosphor reflection ratio increased about15% compared with that. A CRT having smaller dots can be achieved by thepresent invention because high contrast makes a fluorescent areadecreased. Therefore, we can assume that a CRT of the present inventioncan be used as a HDTV and so on.

What is claimed is:
 1. A double layer phosphor screen comprising:a panelhaving black matrix for a CRT; and red, green and blue phosphors on saidpanel, wherein the phosphor is formed on which the black matrix is notformed and said blue phosphor is formed in double layers, and the CIE Ycolor coordinate of said blue phosphor for a first layer formed on thepanel is 0.045 to 0.065, the CIE Y color coordinate of said bluephosphor for a second layer formed on the first layer is 0.075 to 0.095.2. The phosphor screen as claimed in claim 1, wherein said blue phosphorfor said first layer has a diameter of 5 to 10 μm and pigments areattached to it.
 3. The phosphor screen as claimed in claim 1, whereinsaid blue phosphor for said second layer has no pigments.
 4. Thephosphor screen as claimed in claim 1, wherein the ratio of thethickness of said first layer to said second layer is 1:2.
 5. A processfor preparing a double layer phosphor screen comprising the stepsof:forming red and green phosphor dots on a panel having black matrixfor a CRT; coating the slurry of a blue phosphor for a first layer onsaid panel, wherein a CIE Y color coordinate of the phosphor is 0.045 to0.065; coating the slurry of a blue phosphor for a second layer on saidfirst layer, wherein CIE Y color coordinate of the phosphor is 0.075 to0.095; and forming double layer blue phosphor dots by exposing anddeveloping the slurry of blue phosphor for said first and second layers.6. The process as claimed in claim 5, wherein said blue phosphor forsaid first layer has a diameter of 5 to 10 μm and pigments are attachedto it.
 7. The process as claimed in claim 5, wherein said blue phosphorfor said second layer has no pigments.
 8. The process as claimed inclaim 5, wherein the ratio of the thickness of said first layer to saidsecond layer is 1:2.